One of the most important things when working in Photoshop is to preserve the original data...
Here is a link to an excellent tutorial by Dale Glaser

http://www.pacificsites.com/~dglaser...aleSum12N.html

At the end, you'll find as well a link to Steve's building backdoors tut on the same topic:

http://www.thegoldenmean.com/technique/backdoors.html